An organic electroluminescence device (hereinafter, also referred to as organic EL device) can be classified by the emission principle into two types: a fluorescent EL device and a phosphorescent EL device. When a voltage is applied to the organic EL device, holes are injected from an anode and electrons are injected from a cathode. The holes and the electrons are recombined in an emitting layer to form excitons. According to the electron spin statistics theory, singlet excitons and triplet excitons are generated at a ratio of 25%:75%. In a fluorescent EL device which uses emission caused by singlet excitons, the limited value of an internal quantum efficiency is believed to be 25%. A technology for extending a lifetime of a fluorescent EL device using a fluorescent material has recently been improved and applied to a full-color display of a mobile phone, TV and the like. However, as compared with a phosphorescent device, a fluorescent EL device is required to be improved in efficiency.
To cope with this problem, in association with a technology of improving an efficiency of a fluorescent device, a technology of obtaining emission derived from triplet excitons by a phenomenon in which singlet excitons are generated by collision and fusion of two triplet excitons, (i.e., a TTF (Triplet-Triplet Fusion) phenomenon) is disclosed. A blocking layer for effectively causing the TTF phenomenon is required to have a wide gap so as to increase triplet energy. Moreover, since an electron transporting layer is required to be a compound having a high electron tolerance, the electron transporting layer is considered to be preferably a compound formed of a hydrocarbon ring.
Patent Literature 1 discloses an organic EL device in which a host material including an azine ring and a carbazole skeleton is used in a fluorescent emitting layer and BAlq is used in an electron injecting layer adjacent to the emitting layer.
Patent Literature 2 discloses an organic EL device in which a blocking layer is provided adjacently to the emitting layer so as to effectively cause the TTF phenomenon and a fluoranthene derivative is used in the blocking layer.